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Red Seal Auto Body Technician study materials
Red Seal Auto Body Technician study resources

Red Seal Auto Body Technician: Surface Preparation and Body Filling

Red Seal Auto Body Technician · Work through your exam, one topic at a time.

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Surface Preparation and Body Filling

Surface Preparation and Body Filling

This domain tests substrate preparation and filler work. Expect cleaning, sanding, featheredging, primer selection, body filler and glaze, plastic repair, guide coat, block sanding, and corrosion protection. The exam looks for a sequence that produces adhesion and a straight, stable repair.

Core rules

  • Wash the panel, then use a wax and grease remover; contaminants cause fish eyes, poor adhesion, and sandpaper loading.
  • Identify the substrate: steel, aluminum, plastic, e-coat, or existing finish. Use the product system's primer and filler over the correct surface.
  • Featheredge the repair area so the edge is smooth; do not leave a hard ridge that shows through the topcoat.
  • Mix filler and glaze by the manufacturer's ratio; too much hardener can cause shrinkage, cracking, and poor sanding.
  • Apply filler in thin, pressed coats over a properly prepared surface; avoid thick bridges over rust or unrepairable metal.
  • Use guide coat and block sanding to find low and high spots; sand with the recommended grit sequence.
  • Prime bare metal and sanded areas, and restore corrosion protection on the backside of the panel.

Worked example

A repaired fender has a dent filled with body filler, but the technician applies filler directly over sanded e-coat that has been scuffed with 180-grit. Reasoning: the filler system and OEM may require bare metal or a specific primer; applying over an incompatible e-coat can cause poor adhesion. The technician should check the TDS, sand to the specified substrate, apply the recommended primer, then apply filler in thin coats. After blocking, the area is sealed and primed before refinish.

Traps

  • Using lacquer thinner or a contaminated rag for final wipe.
  • Mixing filler with too much hardener to speed the cure.
  • Sanding through e-coat or primer edges.
  • Leaving pinholes that show after paint.
  • Applying filler over rust or a flexible plastic bumper without the correct flex additive.
  • Skipping backside corrosion protection.